recent study from Sweden, comparing family members of an immune person v. comparable non-immune person. 50% reduction in transmission due to immune person. That is (my inference), half of transmissions are within families. This is pre-delta, same effect for disease, one or two vaccines and relatively early after vaccines. They caution that delta transmission may be higher under 1 vaccine.
In other news, US blood donors are now 83% immune as of July, of which 20% are naturally. 65+ are 92% of which 11% naturally (age is wisdom). Blood donors are not the same as overall distribution, of course. I presume most stubborn deniers of everything, do not part with their blood easily.
My projection: number of vaccinated people increases by 3% a month, number of cases by 2% (1% detected, 2x ratio of detected to not detected). So, US will be almost fully immune in a couple of months, not counting the most stubborn population.